Bring a large pot of water to boil, add the pasta. Cook according to package instructions (8-10 minutes). Drain and set aside.
While the pasta boils, set a medium saucepan over low heat. When hot, add olive oil, onion and oregano. Add Shishito peppers and garlic, stirring frequently for 2 minutes. Add half the basil, pour in 1/2 cup water and stir.
Pour the sautéed mixture into the blender. Add rest of basil, plus salt and pepper. Puree until smooth.
Return the pasta to the pot you cooked it in or to the sauté pan. Place over low heat and add sauce. Stir gently and cook until combined. Taste and add more salt and pepper if desired.
Sprinkle fresh basil over the top and serve!