Heat 2 Tablespoons olive oil in a Dutch oven over medium heat until shimmering.
Add ½ yellow or sweet onion (chopped) and 4 cloves garlic (minced); sauté, stirring occasionally, until the onion is tender and translucent, about 4 minutes.
Add 1 lb boneless chicken breast (chopped into bite-size pieces) and cook, stirring often, about 2 minutes (the chicken will finish cooking during the simmer).
Stir in 2 teaspoons chopped chipotle peppers (canned in adobo sauce), ½ teaspoon granulated sugar, the 28 oz. can diced tomatoes (undrained), and 1 cup water; scrape any browned bits from the bottom of the pot.
Increase heat to bring the mixture to a gentle boil.
Reduce heat to low and simmer, partially covered, for 20 minutes, stirring occasionally.
After 20 minutes, confirm the chicken is cooked through (no pink remaining) before serving.