Spicy Chicken Peanut Udon Stir Fry

Name: Spicy Chicken Peanut Udon Stir Fry
Ingredients: 16 ounces fresh (frozen, or dry udon); 1/4 cup vegetable oil (divided plus more if needed); 1 pound ground chicken; 2 shallots (peeled and minced); 8 cloves garlic (peeled and minced); 1 pound Brussels sprouts (trimmed and thinly sliced); 2/3 cup water or stock; 1/4 cup low-sodium soy sauce; 2 tablespoons peanut butter; 1 tablespoon chili oil or sriracha (plus more, to taste); 1 tablespoon mirin; 2 teaspoons sesame oil; Salt and pepper to taste; Crushed peanuts (optional); Chili oil