Preheat oven to 400F. Line a baking sheet with parchment paper.
Arrange the tomato halves, onion, garlic, an jalapeno on the prepared baking sheet. Drizzle with olive oil, sprinkle with oregano, salt, and black pepper.
Roast for 25-30 minutes or until the vegetables are soft and slightly blistered.
Cool the vegetables for three minutes. You can either leave them chunky and mash them together with a fork, or transfer them to a food processor or blender and pulse a few times for a smoother salsa.
Stir in the chopped fresh cilantro. Taste and adjust seasonings with additional salt, pepper, or a squeeze of lime juice if desired.