Prepare 2 cups fettuccine noodles (1/2 package), cooked according to package directions. You'll be cooking half the package of noodles.
While noodles are cooking, preheat the oven to 350F degrees. Spray an 11x7-inch baking dish with nonstick cooking spray. Set aside.
In a large skillet, melt 2 Tablespoons salted butter over medium heat.
Once butter is melted, add in 2 Tablespoons all-purpose flour. Whisk together well until a thick paste forms.
Stir in 2 cups milk. Turn heat up to medium-high. It will start thickening pretty quickly once you turn the heat up. Keep whisking.
Once you see bubbles, turn the heat back down to medium and add 1 1/2 cups shredded mozzarella cheese. If it gets too thick, just splash a bit more milk in there.
Season with 1 1/2 teaspoons garlic salt and 1/2 teaspoon black pepper.
Next, stir in 2 cups fully cooked ham, cubed, 1 cup frozen peas and cooked fettuccine noodles. Mixture will be thick. Stir as best you can to coat all the noodles with the cheese sauce.
Pour combined mixture into prepared baking dish. Set aside.
In a small skillet, over medium-high heat, melt 1 Tablespoon salted butter. Then stir in 1/4 cup dry bread crumbs.
Stir constantly (so they don't burn) until bread crumbs start to brown. Then turn off heat.
Sprinkle browned bread crumbs over the noodles.
Cover with aluminum foil and bake for about 20-25 minutes (until bubbly.)
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Notes
Note: This can be served straight out of the pan without baking it. It firms up when baked but stays ultra creamy when not baked so it's up to your preference.