Step 1

Combine flour, garlic powder, salt, and black pepper in a shallow dish.

Step 2

Roll and coat chicken cubes in flour mixture.

Step 3

Heat 2 tablespoons vegetable oil in a skillet over medium-high heat.

Step 4

Cook and stir chicken in hot oil until not longer pink in the center and juices run clear, 8 to 10 minutes; remove and set aside.

Step 5

Heat 1 tablespoon vegetable oil in the same skillet over medium heat.

Step 6

Cook and stir celery, green peppers, and onion in heated oil until slightly tender, about 5 minutes.

Step 7

Return chicken to the skillet.

Step 8

Whisk ketchup, lemon juice, pineapple, and brown sugar in a bowl; pour into the skillet; bring to a boil.

Step 9

Cook and stir chicken and vegetables in sauce until heated through, 2 to 3 minutes.