First prepare the tomatillo guacamole, cilantro-lime rice, and mango salsa and set aside.
Remove the tough ligament from the side of each scallop and discard. Pat the scallops dry with a paper towel to remove excess moisture. Season both sides of each scallop with salt, and cumin.
In a large cast iron skillet, melt butter over medium-high heat. Allow the skillet to get as hot as possible without burning the butter.
Sear the scallops, turning once, until golden brown on each side, and just cooked through, about 3-5 minutes total. Transfer to a platter and quarter.
To assemble, toast corn tortillas, if desired, over an open flame just until slightly charred. Fill each tortilla with 2 tablespoons rice, 1 tablespoon guacamole, 1 seared and quartered scallop, and top with mango salsa. Repeat with remaining ingredients.
To make guacamole:
Combine the tomatillos, cilantro, avocado, onion, jalapeno, garlic, lime juice, cumin, and salt in a food processor or blender and pulse until combined.
To make the rice:
In a small saucepan, bring the rice, cilantro, broth, rice, and lime juice to a boil over high heat. Reduce the heat to a simmer, cover and cook for 20 minutes, or until the rice is tender. Remove the cilantro sprigs and serve.
To make the salsa:
Combine the mango, tomatoes, minced onion, cilantro, chile, lime zest, and lime juice in a small bowl. Allow the flavors to macerate. Serve as a garnish for the cumin seared scallop tacos.