Begin by placing your nugget-sized chicken pieces in a large bowl. Pour in the buttermilk, making sure all pieces are well-coated. Let this marinate for at least 30 minutes, or up to 2 hours in the refrigerator for the best results.
In another bowl, combine the panko and whole wheat flour (or cornmeal). Mix well to ensure an even coating when you are ready to bread the chicken.
Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper for easy cleanup and to prevent sticking.
Once the chicken has marinated, remove it from the buttermilk, allowing excess to drip off. Dredge each piece in the panko mixture, pressing lightly to ensure the crumbs adhere well. Arrange the coated chicken nuggets on the prepared baking sheet.
Place the baking sheet in your preheated oven and bake for about 20-25 minutes, or until the chicken is golden brown and cooked through. For extra crispiness, you can broil them for the last 2-3 minutes.
While the chicken is baking, prepare your sauce. In a saucepan over medium heat, combine the sweet Thai chili sauce, soy sauce, dark brown sugar, peanut butter, tomato paste, apple juice, rice vinegar, lime juice, fish sauce (if using), garlic, ginger, crushed red pepper, and pepper. Stir to combine, then bring to a gentle simmer.
If you prefer a thicker sauce, mix the cornstarch with cold water in a small bowl, then add it to the simmering sauce. Stir continuously until it thickens to your desired consistency.
Once the chicken is baked, remove it from the oven and transfer it to a large bowl. Pour the sweet and sour sauce over the chicken and toss until all pieces are evenly coated.
Serve the sticky chicken wings warm, garnished with chopped cilantro and cashews for an extra crunch. Enjoy with a side of rice or simply on their own as a tasty snack!