Add oil to a large skillet and heat over medium-high heat. Carefully add corn kernels, season with salt, and cook 3-4 minutes or until lightly caramelized.
Add butter, chili powder, marjoram, and cherry tomatoes; toss to combine, continue cooking for 1 minute. Remove from heat, add lime zest, and season with salt.
Add a little butter and salt to the bread and quickly grill on a grill or grill pan, just until slightly browned with grill marks. Cut each slice into quarters.
Spread the ricotta onto each slice of bread, then top with a spoonful of the corn skillet mixture, pressing into the ricotta slightly so it stays in place.
Sprinkle toasts with crumbled queso fresco and cilantro leaves and serve!