Preheat your oven to 400°F (200°C). Arrange halved fresh tomatoes, sliced onions, and minced garlic on a large sheet pan, drizzle with olive oil.

Roast vegetables for about 30 minutes until golden brown and caramelized.

Transfer roasted vegetables to a food processor, add lemon juice, capers, and olive oil. Blend until smooth.

Boil salted water, add pasta, and cook until al dente. Reserve a cup of pasta water, then drain.

Toss pasta with sauce, add reserved pasta water as needed, stir in melted butter or olive oil.

Adjust seasoning with salt, pepper, and lemon juice. Serve hot, garnished with parsley.