Combine the ground turkey, yellow onion, red and yellow bell peppers, garlic, tomato sauce, black and pinto beans, corn, chili powder, salt, and black pepper in the bowl of a slow cooker.
Cover the slow cooker and cook on low for 6–8 hours or on high for 4 hours.
Once the chili has cooked for 6–8 hours, make the dumplings: In a large bowl, whisk together the eggs, melted butter, milk, and brown sugar.
Add the flour, cornmeal, baking powder, and salt and stir until smooth. Fold in the cheddar cheese.
Using a small ice cream scoop, dollop the dumpling batter on top of the chili. Cover and cook for 2 more hours on low or 1 more hour on high, until the dumplings are puffed and tender.
Scoop the chili and dumplings into bowls and garnish with jalapeño, cilantro, and green onions, if desired.