Preheat the broiler; line a baking sheet with foil. Cook the bacon in a large nonstick skillet over medium-high heat, turning occasionally, until crisp, 6 to 8 minutes. Remove to paper towels to drain; reserve the drippings in the skillet.
Meanwhile, puree 2 scallions, the mayonnaise, 2 tablespoons vinegar and a generous pinch of salt and pepper in a blender.
Stir the garlic into the bacon drippings. Spread out the bread slices on the prepared baking sheet. Top with the garlic mixture and season with salt and pepper (reserve the skillet). Broil until toasted, 1 to 3 minutes.
Chop the kale and put in a large bowl. Add the remaining 1 tablespoon vinegar and rub the kale with your fingers until it softens, about 3 minutes. Return the skillet to medium-high heat and add the olive oil. Add the tomatoes and season with salt and pepper. Cook until lightly browned, about 4 minutes. Remove from the heat; stir in the remaining scallions. Pour over the kale and toss.
Crumble the bacon into the salad. Add the cucumber and about 1/4 cup dressing. Toss well. Serve with the bread and the remaining dressing.