Preheat the oven to 450°F. If you're using a baking stone/steel, place the stone/steel in the bottom third of the oven before you start preheating. Line a large rimmed baking sheet with parchment paper.
In a medium bowl, toss together the Brussels sprouts, olive oil, and Old Bay seasoning. Dump the sprouts onto the prepared baking sheet and spread them out in a single layer, cut-sides down. Roast for 10 to 15 minutes, until the Brussels sprouts are browned but not charred. (Remember: they'll cook more on the pizza!) Remove the sprouts from the oven and set them aside to cool slightly.
Increase the oven temperature to 500°F (if using a baking sheet) or as high as it will go (if using a baking stone/steel). If you’re using a baking stone or steel, switch the oven to Broil on high as soon as it reaches the higher temperature.
Stretch or roll out your dough to a 12- to 14-inch circle, then transfer it to an oiled or parchment-lined baking sheet or a lightly floured pizza peel (if using a baking stone/steel).
Brush the dough lightly with olive oil, then use a pastry brush to spread the Dijon mustard evenly over top, making sure to get it all the way to the edges of the dough. Arrange the roasted Brussels sprouts on top in a single layer, sprinkle with the cheese, and drizzle with half of the cream.
Transfer the pizza to the oven and bake until the crust is golden and the cheese is browned in spots—8 to 10 minutes on the baking sheet, 6 to 8 minutes on the baking stone/steel. Remove the pizza from the oven.
As soon as the pizza comes out of the oven, drizzle the remaining cream over top. Wait a few minutes for the cream to congeal, then dot with Sriracha to taste and squeeze the lemon juice over top. Slice and serve.