Adjust rack to top position and preheat oven to 425 degrees. Wash and dry produce. TIP: For easier cleanup, line a baking sheet with foil.

Cut potatoes into ½-inch-thick wedges. Toss potatoes on a baking sheet with a large drizzle of oil, salt, and pepper. Roast on top rack, flipping halfway through, until browned and tender, 20-25 minutes.

While potatoes roast, halve, peel, and thinly slice onion. Trim and discard root end from lettuce; halve lengthwise and thinly cut crosswise into shreds. Thinly slice tomato into rounds.

When potatoes have 10 minutes left, heat a drizzle of oil in a large pan over medium-high heat. Add onion and cook, stirring occasionally, until beginning to soften, 2-3 minutes.

Add beef* and Fry Seasoning; cook, breaking up meat into pieces, until browned and cooked through, 4-5 minutes more.

Turn off heat and stir in stock concentrate until well combined. Sprinkle cheddar over top and cover pan with a lid to melt cheese.

Halve and toast baguettes (they can go directly on an oven rack). Spread as much ketchup and mayonnaise as you like on cut sides.

Stir beef mixture until cheese is incorporated.

Divide baguettes and potato wedges between plates. Fill baguettes with cheesy beef and as much lettuce and tomato as you like. Serve with any remaining ketchup and mayonnaise on the side for dipping.