Preheat the oven. Preheat oven to 350°F with a rack in the middle position. Line a rimmed baking sheet with parchment paper.
Toast the cracker crumbs. Toss the crushed saltines with melted butter in a 12-inch skillet over medium heat. Cook, stirring often, until lightly toasted, about 3 minutes. Set aside.
10 Saltine crackers, 1 tbsp butter
Prepare the jalapeños. Cut each jalapeño in half lengthwise through the stem, leaving some stem attached to each half. Remove the ribs and seeds, reserving some if you'd like to add heat to the filling.
12 jalapeno chiles
Make the filling. In a medium bowl, combine the cheddar, cream cheese, green onions, lime juice, chili powder, salt, and black pepper. For medium or spicy jalapeños, finely chop some of the reserved ribs and seeds and mix them into the filling according to the Notes below.
1 ½ cups shredded cheddar cheese, 4 ounces cream cheese, 3 green onions, 2 tsps lime juice, 1 tsp chili powder, ½ tsp salt, ¼ tsp fresh black pepper
Fill the jalapeños. Divide the cheese mixture evenly among the jalapeño halves and arrange them on the prepared baking sheet. Sprinkle with the toasted saltine crumbs.
Bake. Bake for 15 to 20 minutes, until the filling is hot and melted and the peppers are tender. The jalapeños will be soft when first removed from the oven but will firm slightly as they cool. Sprinkle with cilantro and serve warm.
2 tbsp fresh chopped cilantro