Season the fish with salt and pepper. In a large nonstick skillet, heat 1 tbsp. oil over medium-high. Add the fish; cook until golden but not cooked through, about 2 minutes per side. Transfer to a plate; sprinkle with the lemon juice.
In the same skillet, heat the remaining 2 tbsp. oil over medium-high. Add the onion and bell pepper. Cook, stirring often, until the vegetables soften, about 5 minutes. Add the tomatoes and the juices from the can, the capers, garlic and oregano; bring to a simmer. Reduce the heat to medium-low. Cover and simmer, stirring occasionally, until the flavors meld, about 15 minutes.
Meanwhile, in a small saucepan, cook the rice according to package directions.
Nestle the fish in the red-pepper sauce. Cover and cook until the fish flakes easily, about 3 minutes. Serve over the rice.