Place eggs in single layer in medium saucepan. Add cold water to cover eggs by 1 inch. Heat over high heat just to boiling. Remove from burner. Cover pan. Let eggs stand in hot water about 12 minutes. Drain immediately and cool completely under cold running water or in a bowl of ice water.
Meanwhile, cook bacon until crisp; drain and crumble. Set aside 1 tablespoon crumbles for topping.
Rinse spinach and basil leaves; pat dry. Reserve 12 spinach leaves for lining egg white halves. Chiffonade remaining spinach by rolling up leaves and cutting across the roll into thin strips. Chiffonade all of the basil leaves in the same fashion.
Seed and dice tomato; set aside 1 tablespoon diced tomato for topping.
Peel eggs and halve lengthwise. Remove yolks and set white halves aside. Place yolks in a small bowl and mash with a fork. Stir in mayonnaise and mustard and salt and pepper to taste. Gently stir in the unreserved bacon, spinach, basil and tomato.
Arrange egg white halves on a serving plate. Place a reserved spinach leaf in the bottom of each egg white half, allowing edges to stick out at the top. Spoon egg yolk mixture on top of spinach leaves in egg white halves. Sprinkle reserved bacon crumbles and diced tomato on top.