Add the bacon to a large skillet and cook over medium-low heat, flipping it as needed, until all the fat has rendered, about 8 minutes. Transfer the bacon to a paper towel-lined plate. Let cool, then crumble.
Meanwhile, stir together the broccoli, scallions, onions and grapes in a large bowl.
Whisk together the mayonnaise, sugar, milk and vinegar in a medium bowl. Taste and season the dressing with salt and pepper.
Add the dressing to the salad, toss to combine and then stir in the mozzarella, almonds and crumbled bacon. Serve immediately or cover and refrigerate until ready to serve, ideally, up to 1 day in advance.
It's best to make this salad a day in advance and refrigerate it, covered, to let the flavors develop.