In a medium bowl, whisk together peanut butter, water, brown sugar, 1 tablespoon soy sauce, fish sauce, curry paste, rice vinegar, ginger, and 2 teaspoons red pepper flakes until smooth. Set aside.
In a large wok or deep skillet, heat 2 tablespoons olive oil over medium high heat. Add onion and cook until fragrant and beginning to soften, about 3 minutes. Add garlic and cook 30 seconds. Add chicken sauté, stirring occasionally, until the middles are no longer pink and juices run clear, about 5 minutes. Remove chicken from pan and set aside.
Add remaining 2 tablespoons olive oil to pan. Add vegetables and mushrooms and saute until crisp-tender, about 6-8 minutes, depending on the veggies selected.
Return chicken to pan. Add reserved peanut sauce and remaining 2 tablespoons soy sauce and 2 teaspoons red pepper flakes. Toss to coat evenly and cook until heated through, about 2 minutes. Stir in peanuts and cilantro.
Serve stir fry with prepared brown rice, quinoa, or whole wheat spaghetti. Garnish with additional chopped peanuts and cilantro, as desired.
Thai red curry paste and fish sauce are widely available at most grocery stores in the Asian food aisle.
To Store. Keep leftover Chicken Stir Fry with Thai peanut sauce in the refrigerator for up to 1 week or freeze for up to 2 months.