In a large bowl, combine masa harina and salt. Gradually add warm water while mixing until a soft, pliable dough forms that doesn't crack at the edges. Cover with a damp towel and let rest for 10 minutes.

In a small saucepan, heat 1 tablespoon of oil over medium heat. Add onion and garlic, sauté for 2 minutes until fragrant. Add black beans and cumin, then mash with a fork until mostly smooth. Cook for 3-4 minutes, stirring occasionally. Set aside to cool slightly.

Divide the masa dough into 8 equal portions. Roll each portion into a ball, then flatten into an oval shape about 1/4 inch thick. Place 1 tablespoon of black bean filling in the center.

Fold the edges of the masa over the filling and pinch to seal completely. Gently reshape into an oval boat shape about 4 inches long, pinching the ends to form points. The tlacoyo should be about 1/2 inch thick.

Heat a large non-stick skillet or comal over medium-high heat. Brush lightly with remaining vegetable oil. Cook tlacoyos for 4-5 minutes per side until golden brown spots appear and the masa is cooked through.

Transfer cooked tlacoyos to a serving platter. Top each with a spoonful of salsa verde, shredded lettuce, sliced radishes, crumbled queso fresco, avocado slices, and a drizzle of Mexican crema.

Garnish with fresh cilantro and serve immediately with lime wedges on the side for squeezing over the top.