In a saucepan, melt butter. Add flour, whisking to create a roux.
Slowly whisk in warm milk until smooth and thickened.
Gradually add the Riopelle, Oka, and cheddar, stirring constantly until fully melted.
Stir in Dijon mustard, lemon zest, tarragon, salt, and white pepper to taste.
Cut through the top shell of each lobster tail lengthwise. Carefully split them in half, exposing the meat.
Brush lobster meat with olive oil, melted butter, minced garlic, lemon zest, salt, and pepper.
Preheat grill to medium-high heat. Lightly oil the grates.
Season striploin steaks with salt and pepper.
Grill steaks 3–4 minutes per side for medium-rare, adding butter, thyme, and garlic during the last minute. Rest steaks for 5–7 minutes before slicing.
Grill lobster tails flesh-side down for 2–3 minutes until lightly charred, flip, and grill shell-side down another 3–4 minutes until opaque and cooked through. Brush with additional garlic butter as they cook.
Boil pasta in salted water until al dente. Drain.
Fold pasta gently into cheese sauce until coated.
Spoon cheesy pasta on to plates.
Top with sliced Alberta striploin and grilled lobster tail halves.
Garnish with fresh parsley, extra lemon zest, or a drizzle of melted butter if desired.