For an easy variation, substitute 2 cups frozen corn and 1 1/2 cups canned black beans (drained and rinsed) for the potatoes, but omit the stock.
Heat oil in large skillet over medium heat. Add onion; cook, stirring often, 5 minutes, or until soft. Stir in cumin, chili powder and potatoes. Cook, stirring occasionally, 2 minutes. Add stock; cook about 15 minutes, or until potatoes are tender and liquid is gone. Season with salt and pepper. Remove from heat.
Heat large nonstick skillet over medium heat; spray with cooking spray. Add one tortilla; sprinkle about 1/4 cup cheese over half of tortilla. Spoon about 1/3 cup potatoes over cheese; top with 2 Tbs. tomato and 1/4 cup more cheese.
Fold tortilla in half, and press down with spatula. Cook about 1 minute, or until underside is golden. Turn over, and cook 1 minute more. Remove, and cut into wedges. Repeat with remaining tortillas; respray skillet as needed.