Preheat the oven to 400 degrees.
Toss the tomatoes lightly with olive oil on a baking sheet. Spread them out into one layer and sprinkle generously with kosher salt and pepper. Roast for 15 to 20 minutes, until the tomatoes are soft.
Transfer the tomatoes to a serving bowl and sprinkle with basil leaves and sea salt. Serve hot or at room temperature.