Finely chop the garlic and chilies, then use the side of your knife to press them together into a rough paste. (Add a pinch of salt to make this process easier.).
Preheat a wok or stainless-steel saute pan over medium-high heat. Add the oil and the garlic-chili paste you just made, and cook for 1 to 3 minutes (be careful not to burn the garlic).
Chop the chicken into small pieces and add them to the pan, cooking until they're lightly browned, about 3 to 4 minutes. Add the soy sauce, red-chili paste, and sugar, and continue to cook until the chicken is done all the way through, another 3 to 4 minutes.
Add the pepper and spinach, and cook until the spinach is just wilted, about 2 minutes.