Preheat a grill on medium-high heat. Clean and oil the grate.
Cut the baguette(s) into thin slices about 1/8 to 1/4 inch thick. Arrange them in a single layer on a large baking sheet. (Note: If you've baked fresh baguettes, allow the loaves to cool completely before slicing. For smaller slices, cut directly across the loaf. For longer slices, cut the baguette on a bias / angle.)
Drizzle the slices with olive oil.(Note: You don't have to cover every square inch of the slices with olive oil. Just aim for greater than 50% coverage. Drizzle enough olive oil that it soaks into the slices, but not so much that it runs through and pools on the baking sheet.)
Season the top side of the oiled slices with a sprinkling of coarse kosher salt, some fresh-cracked black pepper, and a generous dusting of garlic powder.
Grill the slices, plain side down, until toasted and starting to show browned grill marks, about 4 minutes. Flip the slices and repeat on the second side. Then remove and serve.(Note: Watch the crostini carefully during grilling. They can go from perfectly grilled to burned and blackened surprisingly quickly!)