Step 1: Prepare the Filling

1. Heat a small skillet over medium heat. Add the ground beef (or shredded chicken) and chopped onion.
2. Cook for 5 to 7 minutes, breaking up the beef into crumbles, until the meat is fully cooked and the onions are tender. If using shredded chicken, simply cook until the onions soften and everything is well combined.
3. Drain any excess liquid from the skillet.
4. Stir in the shredded pepper jack and cheddar cheese, thawed corn, diced tomatoes, taco seasoning, jalapeño pepper, and chipotle pepper. Mix until everything is well incorporated. Remove from heat and set aside.

Step 2: Prepare the Phyllo Dough

1. Preheat the oven to 375°F (190°C).
2. Place one sheet of phyllo dough on a clean work surface. Lightly brush with melted butter.
3. Cover with another sheet of phyllo and brush it with butter as well. This layering helps create a sturdy base for folding.
4. Keep the remaining phyllo dough covered with a damp kitchen towel to prevent it from drying out.

Step 3: Assemble the Triangles

1. Using a sharp knife or pizza cutter, cut the layered phyllo sheets into three strips (each about 14×3 inches).
2. Place a tablespoon of filling about an inch from one end of a strip.
3. Fold the corner of the strip over the filling to form a triangle. Continue folding like a flag until you reach the end of the strip.
4. Brush the outside of the finished triangle with butter to help seal it and give it a golden, crispy texture.
5. Repeat this process with the remaining phyllo sheets and filling.

Step 4: Bake the Triangles

1. Arrange the assembled triangles on a greased baking sheet, leaving space between them for even cooking.
2. Bake for 12 to 15 minutes, or until the triangles are golden brown and crispy.
3. Remove from the oven and let them cool slightly before serving.

Step 5: Prepare the Salsa-Ranch Dipping Sauce

1. In a small bowl, combine the ranch dressing and salsa. Stir until smooth and well blended.
2. Serve alongside the warm nacho triangles for dipping.