First, prepare the avocado purée. Halve the avocados, remove the pits, and scoop the flesh into a medium bowl.
Add the lemon juice, sour cream, salt, and pepper. Mash everything together with a fork until smooth and creamy.
Cover with plastic wrap pressed directly onto the surface and chill for up to 3 hours.
Position an oven rack a few inches from the heat source and preheat the broiler.
Brush both sides of each tortilla with oil and arrange them in a single layer on a baking sheet (you may need to do this in batches).
Broil the tortillas for 1-2 minutes per side, or until golden and crisp. Watch them closely as they can burn quickly!
Keep the broiler on.
Arrange the crisped tortillas on the baking sheet.
Sprinkle evenly with the minced jalapeño peppers, then cover generously with the grated Monterey Jack cheese.
Broil for another 2-3 minutes, or until the cheese is completely melted, bubbly, and slightly golden.
Repeat with any remaining tortillas.
To serve, transfer the hot chalupas to plates.
Top each one with a generous dollop of the chilled avocado purée. You can spread it, create a design, or simply spoon it on top.
Serve immediately and enjoy!
