Sauté diced potatoes in olive oil with salt, pepper, and paprika for 10 minutes until golden. Set aside.
Sauté onion in the same skillet. Add ground beef, cook until browned, then drain.
Add garlic, taco seasoning, and water. Simmer 3–4 minutes. Stir in cooked potatoes and remove from heat.
Melt butter, whisk in flour to make a roux. Gradually add milk, cook until thick, then stir in cheddar and salt. Keep warm.
Fill tortillas with beef-potato mix and shredded cheese. Roll tightly.
Toast seam-side-down in a buttered skillet, 2–3 minutes per side until crisp and golden.
Slice in half, drizzle with nacho sauce, and garnish with tomatoes and parsley. Serve hot.