Warm the olive oil in a large skillet over medium heat.
Add the onion and cook, stirring occasionally, for 3 to 5 minutes, or until softened.
Add the garlic, cook for 1 minute, then add the tomatoes, capers, salt, and pepper.
Reduce the heat to medium-low and cook for 5 minutes.
Season the tilapia with salt and pepper.
Raise the heat under the sauce to medium and simmer.
Nestle the fillets in the sauce, cover, and cook for 3 minutes.
Using cooking tongs or a fork, turn the fish over and continue cooking, uncovered, for 3 to 5 minutes, or until a fork goes through the thickest part of the fish with no resistance.