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1
To make the marinade, combine all of the ingredients in a bowl and whisk together until combined.
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2
Reserve 1/4 cup of the marinade in an airtight container in the refrigerator.
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3
Put the tenderloin in a large zipper-lock plastic bag and add the remaining marinade.
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4
Seal and shake the bag to make sure the meat is well coated.
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5
Place in a baking dish and refrigerate for 8 hours or up to overnight, turning the bag a few times.
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6
When ready to cook, in a bowl, toss the peppers and onion with the reserved 1/4 cup marinade.
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7
Remove the tenderloin from the marinade, letting the excess marinade drip off, and transfer to a large plate.
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8
Let come to room temperature while you prepare the grill.
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9
Prepare a charcoal grill for medium-high heat, banking the coals on one side of the grill.
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10
Clean and oil the grill grate.
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11
Put a large cast iron frying pan on the cooler side of the grill and add the onions and peppers.
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12
Place the tenderloin over the hotter side of the grill.
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13
Cover the grill and cook, turning the tenderloin a few times, until it is nicely seared and cooked to medium (about 145 degrees F).
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14
Transfer the tenderloin to a cutting board, tent with foil, and rest while you finish the vegetables.
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15
Move the cast iron frying pan to the hotter side of the grill and cook the vegetables, stirring occasionally, until tender.
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16
Set aside.
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17
Thinly slice the tenderloin against the grain, then transfer it to the cast iron frying pan with the vegetables.
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18
Serve right away with warm tortillas, salsa, sour cream, sliced avocado, and crumbled queso fresco.
