Preheat broiler to high. Place baguette halves, cut sides up, on a large, rimmed baking sheet. Whisk together eggs, half-and-half and salt in a large bowl.
Cook bacon in a large nonstick skillet over medium-high heat until crisp. Let bacon cool; crumble. Drain off all but 1 Tbsp. fat. Add egg mixture to skillet and cook, pushing and turning eggs with a big, flexible spatula so they form large curds, until moist but solid, 2 to 3 minutes.
Spoon eggs onto baguette. Top with reserved bacon, cheese and scallions. Broil until cheese has melted, 1 to 2 minutes. Serve immediately.