Whisk together the eggs, half & half, chopped chives, salt and black pepper. Add the crumbled bacon. Melt 1-2 Tbsp of butter in a large skillet and add the egg. Let the egg cook gently over medium heat until cooked through, turning gently as needed
While the eggs are cooking, preheat the oven to broil.
Slice the baguette in half, and butter both sides. Place the bottom piece of the baguette on a baking sheet. Toast the bottom of the baguette in the oven until golden, about 2-3 minutes. Remove from the oven and arrange the cooked egg over the toasted baguette.
Top with the Colby-Jack cheese slices.
Return to the oven with the top piece of the baguette. Lay side by side. Broil until the cheese melts on the egg and the top baguette is toasted and golden.
To assemble, top with fresh spinach and sliced tomatoes. Dress with mayonnaise if desired. Cut into equal potions and serve immediately.