1 Rinse the orange in hot water, wipe dry and finely grate the zest. Squeeze juice from orange.
2 Halve chile peppers lengthwise, remove seeds, rinse and pat dry. Finely chop chiles. Squeeze juice from lime.
3 Combine orange zest and juice, chiles, lime juice, 1 tablespoon oil and the tomato paste in a freezer bag, then seal tightly and turn to mix well.
4 Pat pork dry and place in the marinade, seal bag and turn to coat. Shake bag well. Let marinate in the refrigerator for at least 3 hours.
5 Remove pork from marinade and drain. Cook on a lightly oiled grill until browned all over and cooked through, turning with tongs, about 15 minutes.
6 Remove from grill, cover with aluminum foil and let stand 5 minutes before slicing.