Preheat the grill to medium. Use a wire grill brush to loosen any crud or soot from the grate. Use an oiled side towel to remove any loosened crud.
Put the corn and the tomatillos on the grill and grill until they get charred and black on all sides. Remove from the grill and let cool.
Cut the kernels from the corn cob and scrape any residual bits of corn off the cob. Scrape any really charred bits of skin off the tomatillos and then cut them into 1/2-inch chunks.
In a large bowl, combine the corn, tomatillos, black beans, garlic, scallions, and jalapenos, if using. In a small bowl or measuring cup, combine the vinegar and oil. Pour over the salsa and season with salt, to taste. Taste and adjust the seasoning, if needed. Toss in the cilantro and serve.