Wash and dry jalapeños. Wear disposable gloves to protect against capsaicin. Halve lengthwise, then scoop out all seeds and membranes. For whole roasted peppers, leave intact. Place cut-side up on a parchment- or foil-lined baking sheet. Lightly spray with oil for even browning.

Preheat oven to 450°F. Whole peppers: arrange on a baking sheet, roast 12–20 min, turning halfway, until skins are fully charred and blackened. Halved with filling: bake at 400°F for ~20 min until cheese melts and peppers are tender. Halved unfilled: roast at 450°F for 12–15 min until edges char and flesh softens. Watch closely — ovens vary. Look for visible browning or charring as your doneness cue.

Cover roasted peppers with foil or plastic wrap immediately after removing from oven. Steam 15–20 minutes. Peel charred skin under cool running water or by hand. Remove stem and seeds. Serve warm or cut into strips. Store leftovers in an airtight container in the fridge up to 4 days.