Preheat oven to 400ºF. Place tomatoes on a lightly oiled baking sheet. Sprinkle with salt and pepper and drizzle with the oil. Roast for about 30 minutes or until concentrated and beginning to caramelize. When cool enough to handle, roughly chop the tomatoes.
While the tomatoes are cooking, bring a pot of salted water to a boil. Cook the pasta according to package directions. Drain and reserve.
Bring another pot of salted water to a boil. Cook the collards until tender (about 10 minutes). When cool enough to handle, roughly chop. Reserve.
Heat a large saucepan over medium heat. Add the butter and onions and cook until softened (about 3 minutes). Whisking constantly, stir in the flour, taking care the flour doesn’t brown. Continue to cook for 2 minutes. Whisk in the milk. It will thicken as it gets hot. Whisk constantly; any lumps will smooth out. Cook for 5 – 7 minutes. Mixture will bubble and thicken and when it no longer changes in consistency, it’s done. Stir in nutmeg, cayenne and cheese. Season to taste with salt and pepper.
Stir in pasta, collards and ham. Fold in tomatoes. Spread into a 9” x 9” pan. Sprinkle with breadcrumbs. (Mac ‘n’ Cheese can be made ahead to this point and refrigerated or frozen.) Bake for 15 minutes or until heated through.