1. Preheat your oven and a pizza stone (or cast-iron skillet) to 500°F (or up to 550°F if your oven can go higher.)
2. Heat the olive oil in a heavy-bottomed skillet. Add the onions, rosemary, garlic, salt and pepper, stirring to evenly coat with oil, and cook gently over medium low to low heat (lowering if necessary to prevent over-browning) for about 20 minutes, until the onions are softened lightly browned. Do not caramelize the onions completely, or they will scorch in the oven.
3. Dust your work surface with flour and gently stretch your pizza dough into a circle, about ⅛-inch thick. Generously cover a pizza peel or cookie sheet with semolina or cornmeal.
4. Spread the onion mixture (including the oil) to within ¼-inch of the edges of the crust. Arrange the cooked bacon over the top of the onions. Give the pizza a gentle shake to be sure the dough isn't sticking. If it is, carefully lift that area and sprinkle more semolina or cornmeal underneath to fix it.
5. Slide the dressed dough onto the hot pizza stone and bake until it is evenly browned and crisp underneath, 8 to 15 minutes. Use the pizza peel to transfer the Pissaladière to a cutting board.
6. Top immediately with large chunks of goat cheese, and allow to melt slightly onto the hot Pissaladière.
7. Cool for five minutes, cut into wedges, and serve warm or at room temperature.