In a straight-sided, 10-inch pan, heat the olive oil over a medium flame. Add the onions, peppers and garlic and cook until the vegetables are soft, about 5 minutes. Season with salt and pepper. Add the white wine and tomato puree and reduce the liquid by two-thirds, about 8 minutes.
Add the smoked paprika and saffron, along with the bay leaf. Fold in the rice and make a bed for the seafood to sit on. Add the mussels, clams and shrimp and season again. Cover the pan, turn the heat to high and cook until the shellfish is finished and the bottom of the pan has started to caramelize the rice, about 5 minutes. This is a challenging step and is based on timing.
Finish the paella with fresh parsley, and serve with lemon wedges on the side.