Place chicken breasts in the bottom of your crockpot.
In a small bowl, whisk together pineapple juice, brown sugar, soy sauce, and garlic.
Pour the mixture over the chicken.
Cover and cook on low for 6 to 7 hours or on high for 3 to 4 hours.
If you prefer a thicker sauce, mix cornstarch with a little water and stir into the sauce during the last 30 minutes of cooking.
Season with salt and pepper to taste.
Serve the chicken over cooked rice, spooning sauce on top.
Garnish with chopped green onions before serving.