Preheat the oven to 400 degrees F. Spread the cashews on a baking sheet and roast in the oven until golden.
Toss the tomatoes, 1 tsp of olive oil, and a sprinkle of sea salt together. Then, place on a baking sheet and roast in the oven until the skins of the tomatoes pop open (about 8-10 minutes).
To make the pesto, put the roasted cashews in the food processor and grind until they are like little breadcrumbs. Add about 2/3 of the basil leaves, 1 pinch of salt, and then enough of a drizzle of olive oil to make a soft paste-like sauce.
Bring a big pot of water to boil. Add the pasta and cook as the package directs for al dente pasta (soft but still a little firm in the middle). Drain all but 4 Tbsp of the cooking liquid (keep this in a container for now). Put the pasta back into the cooking pan. Add the pesto, the 4 Tbsp of left over cooking liquid, and a splash of olive oil. Gently mix together.
Lastly, add the tomatoes and chopped up left over basil leaves. Serve nice and warm.