Heat large, heavy-bottomed pot over medium heat. Once hot, add bacon pieces and cook until crispy. Transfer bacon to plate lined with paper towels, and drain all but 2 tablespoons of drippings from pot.
Add onion, celery, and carrots to pot with 2 tablespoons bacon drippings. Cook, stirring occasionally, until veggies are softened, approximately 5 to 6 minutes. Add garlic to pot. Stir and cook until softened, approximately 1 to 2 minutes.
Add all-purpose flour to pot. Stir well to combine and cook until flour mixture is lightly browned.
Stir in bell pepper, potatoes, chicken, and chicken broth. Once mixture is combined, let simmer uncovered 10 minutes.
Remove pot from heat. Stir in half-and-half, then return pot to heat and stir in frozen corn. Let chowder simmer another 10 minutes or until thickened. If desired, remove some potatoes from pot and transfer to bowl. Mash potatoes well then stir back into chowder to thicken consistency even more.
Add bacon pieces to pot, saving some for garnish. Portion chowder into serving bowls, garnish with remaining bacon pieces and chopped green onion, and serve warm.