Preheat the oven to 400 degrees. Coat a baking dish with olive oil cooking spray.
Add the tomatoes, onion, and garlic to the baking dish then drizzle with olive oil and season with crushed red pepper flakes and freshly cracked black pepper, to taste.
Place into the oven and roast for 20-25 minutes, or until onion is tender and the tomatoes are ready to burst. Remove from the oven and spoon out the garlic cloves. Set aside to cool then peel the skin and slice thinly. Place the sliced garlic back into the tomato mixture. Taste and season with sea salt, if needed.
Place a slice of French bread into the oven for a few minutes, or until toasted.
Spoon the tomato mixture on top of the toast then sprinkle with fresh basil and drizzle with balsamic, if desired. Serve immediately. Enjoy.