Position a rack in the center of the oven and heat the oven to 450°F. Let the pizza dough stand at room temperature while you roast the squash.
In a large bowl, toss the squash with 2 Tbs. of the maple syrup, 1-1/2 tsp. of the oil, 1/4 tsp. salt, and 1/8 tsp. pepper. Spread it in a single layer on a large heavy-duty rimmed baking sheet and roast until tender and lightly browned, about 12 minutes. Let cool to warm.
Dust another large heavy-duty rimmed baking sheet with semolina or cornmeal. On a lightly floured work surface, roll the dough into a 1/4-inch-thick oval; transfer to the prepared baking sheet.
Lower the oven temperature to 425°F. In the large bowl, gently toss the squash, onion, thyme, 1-1/2 tsp. of the remaining oil, 1/2 tsp. salt, and 1/4 tsp. pepper
Scatter the squash mixture evenly over the dough, then scatter the sausage and teaspoonfuls of ricotta all over. Sprinkle with the pecorino and bake until the crust is golden-brown and crisp, about 30 minutes.
In a large bowl, whisk the remaining 1 Tbs. syrup and 1 Tbs. oil, the vinegar, 1/2 tsp. salt, and 1/4 tsp. pepper. Add the chard to the bowl, and toss to coat. Scatter the chard over the flatbread. Cut into pieces and serve.