Prepare macaroni according to package directions, taking extra care not to overcook. Pasta should be cooked al dente, or slightly chewy.

Drain pasta and add bell pepper to colander, tossing to mix. Set aside. Bell pepper will soften slightly but maintain its crunch.

For the roux, melt butter in large saucepan over medium-low heat. Sprinkle flour in a couple tablespoons at a time, whisking constantly. Continue whisking and cook about 4 minutes, until mixture is golden-brown.

Slowly add in milk and cream, whisking constantly. Bring to a low boil over medium-high, still stirring. Reduce to a simmer, cooking about 3 more minutes, until sauce is thick and coats the back of a spoon.

Stir in salt, mustard, paprika and nutmeg.

Now, add cheese in batches, waiting until one batch melts before adding more. Continue stirring and adding cheese until it’s gone. Taste your sauce and add more seasonings if necessary. Remove from heat.

Carefully stir in macaroni, bell peppers and tuna until ingredients are mixed well. Serve, garnishing with parsley and a squeeze of lemon.