Preheat oven to 400 F / 200 C.
Clean and cut red bell peppers into quarters. (watch video to see the best way to cut peppers). Cut onion into quarters. Season with 2 tablespoon olive oil, salt and pepper. Toss well to coat and arrange the peppers skin side up.
Bake seasoned peppers and onions in the middle rack for 20-25 minutes, until you see small charred marks on the peppers.
Let the peppers cool down for 10-15 minutes. ( ref note-1)
Add roasted peppers, onion, and cream cheese to a blender jar. Rinse the baking tray with a 1/3 cup of water to release the caramelized brown bits and add it to the blender. Blend everything into a smooth sauce. (ref note -2)
Bring a large pot of water to a boil and salt it well. Cook bucatini as per package instructions.
While the pasta is cooking, melt butter in a large skillet. Saute minced garlic and chilli flakes for 30 seconds.
Add tomato paste and cook on low heat for about 1 minute until it is slightly caramelized.
Stir in the roasted red pepper sauce and cream cheese (if not added to the peppers while blending). Mix everything well and let it simmer for 2-3 minutes.
Add in cooked bucatini and 1/2 cup pasta cooking water to thin out the sauce. season with salt and pepper to taste. Toss to coat the pasta with sauce.
Serve with fresh chopped basil and freshly grated parmesan cheese.