Heat oil in a sauté pan over medium-high heat. Season chicken with salt and pepper and cook until browned on all sides. Place the browned meat in the slow cooker, along with the dried chili peppers.
Combine water, soy sauce, vinegar, brown sugar, hoisin sauce, garlic, and ginger in a bowl. Stir until well combined. Pour over the chicken and peppers in the slow cooker. Cover and cook on low for 4 hours.
Combine the cornstarch and water. Whisk until smooth. Add this mixture to the chicken at the end of its cooking time, and let warm through for 5-10 minutes. The sauce will thicken.
While the sauce is thickening, sauté the red pepper and zucchini in oil, until softened, but still crisp. Add the peppers, zucchini and peanuts to the slow cooker and stir gently to combine. Garnish with chopped green onions and serve immediately, over rice, if desired.