Pat chicken thighs dry with paper towels then season both sides with salt and pepper.
In a large, heavy-bottom pot, heat up olive oil over high heat. Place chicken thighs into skillet, skin side down and sear until skin is crispy and browned, about 7 minutes. Then flip and cook the other side, another 7 minutes. Remove chicken and let rest on a plate.
Reduce heat to medium then add onion and bell peppers. Sauté until softened, about 3 minutes. Add the diced tomatoes, saffron threads, rice, and chicken stock. Stir to incorporate then cover pot and reduce to a simmer, stirring frequently so rice doesn't stick to bottom of pot.
Continue to cook until all liquid is absorbed and rice is cooked through. About 25-30 minutes, depending on the type of rice you have. Add the olives and frozen peas and stir to incorporate and cook until peas are warmed through.
Add the chicken back in to the pot when rice is just about done to heat through the chicken and finish cooking, if it is still slightly raw near the bone.
Season rice with salt and pepper then serve immediately.
Notes
You can store leftover arroz con pollo in an airtight container in the refrigerator for up to 5 days. Reheat it in the microwave or in a covered skillet with a splash of oil to keep it from sticking.