Preheat oven to 375°. Spray an 11x8-inch baking dish with cooking spray.
For greens: In a small Dutch oven, heat oil over medium-high heat. Add onion; cook until lightly browned, 2 to 3 minutes. Add garlic; cook for 1 minute. Add collard greens, broth, salt, and red pepper. Cover, reduce heat, and simmer until tender, about 12 minutes. Uncover; cook over medium-high heat until most of liquid is evaporated. Stir in pork and vinegar. Spoon into prepared pan.
For grits: In a Dutch oven, bring milk, broth, salt, and pepper to a boil over medium-high heat. Reduce heat to medium-low. Whisk in grits. Cook, partially covered and stirring occasionally, until thickened and tender, about 6 minutes.
In a small bowl, place eggs. Whisk ½ cup hot grits into eggs. Whisk egg mixture into remaining hot grits. Add 1 cup Monterey Jack, stirring until cheese is melted. Spread grits over collard green mixture. Loosely cover with foil.
Bake until set, about 25 minutes. Uncover; sprinkle with shredded pork, Cheddar, and remaining ½ cup Monterey Jack. Bake until cheese is melted, about 3 minutes more. Sprinkle with crushed onions. Garnish with pepper, if desired.
Recipe by Taste of the South at https://tasteofthesouthmagazine.com/smoked-pork-greens-and-grits-casserole/