Place uncooked macaroni in a large pot of salted boiling water and cook until *just on this side of raw* al dente (you don't want mushy overcooked pasta for this!)
Spread macaroni in a 1 1/2-quart casserole dish. Top with spinach and peas.
Toss broccoli, squash, and carrots with 1 tbsp oil, then spread evenly on a cookie sheet, roast slightly.
Meanwhile, in a medium saucepan add butter and saute horseradish and lemon grass until fragrant, then add remaining ingredients.
Add roasted vegetables to the casserole dish with noodle mixture; stir to mix.
Stir cheese sauce over low heat until cheese is completely melted. Pour over noodle mixture.
Top with reserved shredded cheese and then top with seasoned panko breadcrumbs cut with softened butter, if desired.
Bake in 350°F oven 25 minutes or until hot and bubbly.
Make sure your noodles are not fully or over cooked, or they will turn into mush. Pre-packaged shredded cheese usually has corn/potato starch or cellulose added to prevent caking. I do recommend shredding as needed for this reason.