Preheat your oven to 325F. Line two baking pans with parchment or foil. Place the tomatoes, cut side up, on the pans. Nestle the onion and garlic on the pans. Drizzle the tomatoes with the oil, then use your hands to lightly mix and coat them. Sprinkle the tomatoes generously with kosher salt and freshly ground black pepper. Transfer the baking pans to the oven and roast for 2-3 hours, or until most of the tomato juices have evaporated and the tomatoes are browning at the edges. For a looser and saucier sauce, you can stop before the tomatoes are browning, while they're still releasing their juices.

When the tomatoes are ready, allow them to cool for about 10-15 minutes. Transfer the tomatoes and onion to a blender or food processor. Carefully (the cloves will still be hot), squeeze the roasted garlic flesh out of the cloves and into the blender. Blend the sauce until it has a texture you like; I like to leave my sauce a little chunkier, but you can also blend it to a smooth purée if you prefer. Taste and add salt and pepper as needed, or add a pinch of crushed red pepper flakes if desired.

Bring a large pot of salted water to boil. Add the orzo and cook according to package instructions. Drain, reserving a little (about 1/2 cup) of the pasta water. Add the cooked orzo and chickpeas to a large bowl, then add the pasta sauce. Fold the ingredients together, then add the basil and mix everything well. If you'd like it to be creamier or looser, add a bit of the pasta cooking water and mix again. Serve, with some vegan parmesan or hempesan if you like.