Prep. Paella assembly moves quickly so make sure you have all your ingredients measured and cut in advance (mise en place). Begin by cutting the boneless, skinless chicken thighs into bite sized chunks or strips. Remove the stem, core, and seeds from the bell pepper then slice into strips.
Remove the ends and skin from the onion and then coarsely chop.
Press or mince the garlic.
Fire up. Preheat a gas grill to medium high. If you are using charcoal, you'll need enough coals for about 90 minutes of cooking. Prepare enough coals to cover the lower grate with only one layer, shoulder to shoulder. If you are cooking indoors, preheat the oven to 400°F (204°C) and put a rack in the lowest position.
Cook. Put the broth and tomatoes in a pan with the saffron and heat it on the grill until it is simmering. Don't let it boil because you need all the liquid. This step helps extract the saffron's flavor, and we don't want to add cold broth to the paella.
Sprinkle the chicken generously with salt and pepper.
Put a 12- 14-inch (30 to 35 cm) pan over the hot part of the grill, let it heat for a minute, and add the oil. There should be enough to cover the bottom about 1/8-inch (3.2 mm) deep. If not, add more. You don't want to skimp on the oil because it is necessary to form the socarrat. Make sure the grill is level so the oil covers the entire pan evenly. If you are cooking indoors, turn the burner on high. It will cool off soon after you add the meat. After a minute or so, when the oil is hot and shimmering, place the chicken parts in the oil, and cook. Don't touch the meat for about 5 minutes so it has a chance to turn golden while in contact with the hot pan. Stirring too frequently will prevent browning. When it is golden on one side, stir, scraping the crunchy stuff the French call fond off the bottom, and turn the chunks over to brown on the other side. If the pan is not hot enough to fry, then you need more heat.
When the second side of the chicken chunks are golden add the chorizo, green beans, onions, and half the pepper strips. The veggies will give up some water so cook until it evaporates as steam and you can hear the oil hissing and frying. Add the paprika, garlic, and rice, and cook for 1 minute, stirring to make sure the rice is coated with oil. If you are using dried rosemary and thyme, add it now. If you are using fresh, it goes in later. Gently add the broth/tomato/saffron mix. Do not stir because you want the rice under the liquid. Rice on top will not cook properly. Don't worry if a few grains float. If you stir you will get risotto, which is a thick pasty mass. Cook for about 10 minutes or more with the lid of the grill closed and do not stir. If you are cooking indoors, place it in the 400°F (204°C) oven on the bottom rack now.
After 10 minutes, sprinkle ther fresh rosemary and thyme on top and lay the remaining pepper strips on the surface in a pinwheel and cook another 10 minutes until the rice has absorbed the liquid and is no longer runny. Taste a small forkful. The rice should have some chew, buy not be hard, called al dente. Nor should it be mushy or gummy. If it is still hard and the liquid is gone, add water or more broth, 1/4 cup (60 mL) at a time.
When the rice is done, push a fork in and look at the bottom of the pan to see if the rice crispies, the socarrat, are forming. If not, and this is optional, put it over direct heat or on a burner on medium high heat for about 3 to 5 minutes. Rotate the pan every minute or so to prevent hot spots. You should hear the rice on the bottom crackle. This part is crucial: You have to watch so it does not burn badly, a little black is OK, but not a lot. Remove the pan a minute or two after the rice begins to stick, especially if you are using a cast iron pan or a pan with a heavy bottom. Do not wait for it to turn brown. Cast iron will hold heat and continue to cook long after you remove it from the heat. A little blackening is OK, but don't let it get a lot of blackening. It is better to not have any scorched rice than to have a burned tasting meal.
If you are going to garnish with chopped parsley, sprinkle it on now. Remove the pan from the heat and put the cover on or drape a towel over the pan and let it rest for at least 5 minutes. If you don't have a cover, use aluminum foil or a plate.
Serve. To serve, place it on a trivet or a very thick stack of pot holders or placemats or even towels so it does not scorch or crack your table. In Spain many families eat right from the pan!