To make the marinade, blend 1/3 cup olive oil, the juice of 1 large orange, 1/4 cup cilantro leaves and stems, 4 garlic cloves, 2 chipotle en adobo, and 1 teaspoon kosher salt until combined. It will still probably be pretty chunky, that’s cool!
Add the flank steak to a shallow bowl or pyrex and pour the marinade over top. Flip it over to make sure it gets coated all over. Marinate for at least 30 minutes at room temperature, or up to 36 hours in the refrigerator.
Just before grilling, toss 2 halved peaches, 3 halved limes, and 1 large shallot into the marinade with the steak and toss to coat.
Preheat an outdoor grill to medium-high (about 450°F) and oil the grill grates. (see notes on how to cook without an outdoor grill).
Remove as much marinade from the steak as possible, any excess will cause the grill to flare up. Grill the steak, covered, for 5 minutes on the first side, then flip and cook for an additional 3 to 4 minutes, covered, for medium-rare. The best way to tell if your steak is ready? USE A MEAT THERMOMETER. Here’s my favorite. When the thermometer reads 135°F. pull it off the grill and let it rest for 10 minutes. Meanwhile, grill the peaches, shallots, and limes for about 3 minutes per side, or until charred and tender.
While the steak rests, dice the peaches and shallots and toss with the juice of two grilled limes (saving 1 for the mashed avocado), 1/4 teaspoon salt, 1/4 cup chopped cilantro, and 2 tablespoons chopped mint.
To make the mashed avocado, mash the avocado until very smooth in a bowl along with the juice of 1 grilled lime and 1/8 teaspoon salt.
Chop the steak into small cubes.
Char the tortillas on the grill for about 20 seconds per side, or directly over the open flame of a gas stovetop. Or, to make things easier, wrap the entire stack of tortillas in a damp paper towel and microwave for 20 seconds.
Add the avocado mash, steak, and peach salsa to a tortilla. Enjoy!