Rub fish with olive oil and lemon juice. Season with salt and pepper. Heat a couple of tablespoons of olive oil in a large skillet over medium-high heat. Add fish and brown on one side, about 4 - 5 minutes. Flip over and cook for 2 minutes more. Move fish to one side of pan. To other side, add onion and next 5 ingredients. Cook for 2 minutes more. Remove fish from pan before overcooking. To pan, add spinach, tomato and 2 - 3 tablespoons more olive oil. Heat until spnach starts to wilt.