1. To prepare pork, combine first 5 ingredients in an airtight container, stirring until sugar dissolves. Add pork; seal and refrigerate 8 hours or overnight. Remove pork from brine; pat dry. Discard brine.
2. Cook bacon in a nonstick skillet over medium heat until crisp. Remove bacon from pan; crumble. Add 1/2 cup onion and next 5 ingredients (through 1 minced garlic clove) to drippings in pan; cook 8 minutes or until squash is tender and liquid evaporates, stirring frequently. Stir in bacon.
3. Cut 1 (1-inch) horizontal slit through thickest portion of each pork chop to form a pocket. Stuff about 3 tablespoons vegetable mixture into each chop. Sprinkle both sides of chops evenly with 1/4 teaspoon salt and 1/4 teaspoon black pepper. Heat oil in a large cast-iron skillet over high heat. Add pork to pan; cook 3 minutes on each side or until browned. Remove pork from pan; reduce heat to medium-low.
4. To prepare sauce, add 1 1/2 cups onion to pan; cook 4 minutes or until browned, stirring frequently. Add celery, jalapeño, and 1 garlic clove to pan; cook 3 minutes, stirring constantly. Stir in flour; cook 1 minute. Add 1/2 cup broth and 1/2 cup water, stirring until flour dissolves. Add tomatoes; increase heat to medium-high. Return pork to pan; simmer 10 minutes or until desired degree of doneness.
5. To prepare grits, bring 2 1/2 cups water and 1/8 teaspoon salt to boil in a saucepan. Slowly add grits, stirring constantly. Reduce heat, and simmer 20 minutes or until liquid is absorbed, stirring frequently. Remove from heat; stir in butter and 2 tablespoons broth. Serve with pork and sauce.