½ cup finely crushed butter crackers (such as Ritz), plus more for serving
1 tablespoon melted unsalted butter
Preheat the oven to 400 degrees. In a large bowl, mix together the cream cheese, cheddar cheese, mayonnaise, horseradish and Old Bay until relatively smooth. Sprinkle with the lemon juice, add the crab and gently fold it in.
Stir in the scallions and bell pepper until just combined. Spread the mixture into a 1 quart oval baking dish.
In a small bowl, toss the cracker crumbs with the melted butter and sprinkle over the top of the baking dish.
Bake until brown and bubbly, about 15 to 17 minutes.