Fried Udon Noodles With Shrimp and Spicy Peanut Sauce

Name: Fried Udon Noodles With Shrimp and Spicy Peanut Sauce
Ingredients: 1 cup natural peanut butter; 1-inch chunk fresh ginger; 1/4 cup rice vinegar; 1/4 cup reduced-sodium soy sauce; 1/4 cup water; 1 clove garlic; 1/4 teaspoon ground black pepper; Hot sauce, to taste; 4 tablespoons sesame oil, divided; 1 large yellow onion, thinly sliced; 2 large red bell peppers, cored and thinly sliced; 8-ounce package udon noodles; 1 pound shelled raw shrimp, patted dry; 1/2 cup chopped peanuts; 2 scallions, green and white parts, thinly sliced