Place bacon in a large skillet; heat over medium-high. Cook, turning occasionally, until all fat is rendered and bacon is crispy, about 8 minutes. Drain on paper towels.
Place tomatoes and arugula in a large bowl. Add olive oil, vinegar, and pepper; toss gently.
Spread 1 tablespoon mayo on each toasted bread slice. Top evenly with tomato-arugula mixture and cooked bacon. Serve open-faced.