Whisk the mayonnaise, chives, garlic, lemon zest, 1/4 teaspoon salt and few grinds of pepper in a medium bowl until combined. Refrigerate until ready to use.
Cook the bacon in a large nonstick skillet over medium heat, flipping, until crisp and browned, about 10 minutes. Drain on a paper towel-lined plate.
Wipe out the skillet and heat the canola oil over medium heat. When the oil begins to smoke slightly, remove the skillet from the heat and add the ramps in a single layer. Return the pan to the heat and season with salt and pepper. Cook the ramps over high heat for 30 seconds, stirring constantly, to wilt them. Transfer them to a plate and drizzle with the lemon juice.
Toast the bread and spread with butter. Spread a tablespoon of the chive mayonnaise on each slice of bread. Top 4 bread slices with the bacon, ramps and tomato. Top with the remaining bread.
If the ramp bulbs are large, cut them away from the green tops and cook for a few minutes longer until tender.