Combine ground chicken, panko, beaten egg, minced garlic, and salt in a large bowl. Mix gently with your hands until just combined - overmixing creates tough meatballs. The mixture should hold together but still feel light and slightly sticky.

Roll the mixture into 20-24 walnut-sized balls. Heat vegetable oil in a large skillet over medium-high heat. Brown meatballs in batches, turning carefully to create golden crusts on all sides. This takes about 6-8 minutes total. The meatballs don't need to cook through completely - they'll finish in the curry sauce.

In the same skillet, sauté diced onion until softened and translucent, about 3 minutes. Add yellow curry paste and stir constantly for 30 seconds until fragrant. This blooming step intensifies the curry flavors dramatically.

Slowly pour in coconut milk, whisking constantly to prevent lumps. Add fish sauce and brown sugar, then bring to a gentle simmer. The sauce should coat the back of a spoon. Taste and adjust seasoning - you want a balance of creamy, spicy, and slightly sweet.

Return meatballs to the skillet along with sliced bell peppers. Simmer for 8-10 minutes until meatballs are cooked through and peppers are crisp-tender. The internal temperature of meatballs should reach 165°F.