Sear the chicken: Heat the olive oil in a large paella pan (or a wide, shallow pot) over medium-high heat. Add the chicken pieces and sear on all sides until golden brown. Remove the chicken from the pan and set aside.
Sauté vegetables: Add the onion and red bell peppers to the pan and cook for 5-7 minutes, until softened. Add the minced garlic and grated tomatoes and cook for 2 minutes more, until fragrant.
Add rice and saffron: Add the paella rice to the pan and stir to coat the grains with the oil and vegetables. Add the saffron threads and stir for 1 minute.
Add broth and wine: Pour in the hot chicken broth and white wine (if using). Bring to a boil, then reduce heat to low and simmer, uncovered, without stirring, for about 20 minutes.
Add seafood: Nestle the chicken pieces back into the rice. Add the mussels and clams, pushing them slightly into the rice. Arrange the shrimp on top. Continue to simmer, uncovered, without stirring, for another 15-20 minutes, or until the rice has absorbed most of the liquid and the seafood is cooked through.
Add peas: Stir in the frozen peas during the last 5 minutes of cooking.
Rest: Remove the paella from the heat and cover it with a clean kitchen towel. Let it rest for 10-15 minutes. This allows the rice to absorb any remaining liquid and become perfectly tender.
Garnish and serve: Garnish the paella with lemon wedges and chopped parsley. Serve immediately.