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Adjust rack to top position and preheat oven to 425 degrees. Wash and dry produce.
Halve, peel, and dice onion into ¼-inch pieces. Halve celery lengthwise; dice into ¼-inch pieces. Drain and rinse cannellini beans and kidney beans. Roughly chop parsley.
Heat a drizzle of oil in a large pot over medium-high heat. Add sausage or turkey and cook, breaking up meat into pieces, until browned and cooked through, 4-6 minutes. Transfer to a plate. Reserve pot.