Season the chicken thighs with salt and pepper. Add 1 tbsp oil to each of two 12-14 inch skillets or paella pans set over medium-high heat. When oil is hot, add half of the chicken thighs to each pan and brown on both sides, 15-20 minute Transfer to platter.
While the chicken is browning, toast the saffron threads in a 2 qt saucepan. Remove from heat and crush the threads with the back of a spoon. Add 1/2 cup chicken broth and bring to a simmer over medium heat. Remove from heat and let steep for 10 minutes. Add 5 1/2 cups additional broth to the saffron infusion and bring to a simmer, hold until needed over low heat.
If using turmeric instead of the saffron threads, pour 6 cups chicken broth into a 2 qt sauce pan, add the turmeric, and bring to a simmer, hold until needed over low heat.
Divide the green beans and artichoke hearts between the two pans and saute for 5-6 minutes. Transfer beans and hearts to the platter with the chicken.
Remove all but 1 tbsp of fat from each pan and divide the onion and garlic between the pans. Saute until the onion is translucent. Divide the pepper flakes and the smoked paprika between the two pans and saute for 30-60 seconds. Add the tomatoes between both pans and saute until the liquid from the tomatoes has evaporated and the mixture is thickened, about 5-7 minutes more.
Sprinkle 1 1/2 cups of rice over the onion mixture in each pan. Pour 3 cups of the hot broth evenly over each pan of rice, then arrange the chorizo, green beans and artichoke hearts on the rice. Nestle the chicken thighs into both pans and bring to a boil.
Reduce heat and simmer rapidly until the rice appears on the surface of the mixtures, about 5-6 minutes. Arrange the roasted red pepper slices over both pans. Divide the shrimp between both pans and push the shrimp down into the rice.
Continue simmering until all the liquid has been absorbed and the rice is al dente, another 8-10 minutes. If all the liquid has been absorbed but the rice is not done, add a little more broth and cook a few minutes more.
Cover the pans with aluminum foil and cook gently for another 2 minutes to ensure that the top layer of rice is cooked evenly. With the pans still covered, raise the heat to medium high and cook until the bottom layer of rice begins to brown. You may hear rice crackling, which is normal, but if the rice begins to burn, remove the pans from the heat immediately.
Check the chicken for doneness. Sprinkle the peas over each pan and let stand, covered, for 5-10 minutes.
While the paella is standing, bring the remaining chicken broth (or water if you used all of the broth earlier) to a boil in a medium saucepan and add the clams or mussels. Cover and simmer for 3-4 minutes or until the clams/mussels have opened. Arrange the opened clams/mussels over each pan of paella, discarding any that did not open. Serve directly from the pan with wedges of lemon to squeeze over the rice.