Combine the sugar, water, cinnamon stick, and cloves in a saucepan. Bring to a boil over medium-high heat, stirring until the sugar dissolves. Reduce heat and simmer for 5 minutes. Keep the syrup hot over low heat until needed.
Heat the olive oil in a wide, heavy-bottomed pot over medium heat. Add the semolina all at once. Stir continuously with a wooden spoon for 8-12 minutes until the semolina turns golden-brown and smells nutty and fragrant. The color should deepen significantly from white to golden. Do not leave the pot or stop stirring.
Remove the cinnamon stick and cloves from the syrup. With the semolina still on the heat, pour the hot syrup into the pot in one steady stream while stirring vigorously. The mixture will bubble dramatically and may spatter. Continue stirring until the halva thickens and begins to pull away from the sides of the pot, about 2-3 minutes.
Fold in the walnuts if using. Working quickly, pour the halva into a lightly oiled Bundt pan, ring mold, or individual ramekins. Smooth the top. Cover loosely with a clean kitchen towel and let rest for 15-20 minutes.
Place a serving plate over the mold and invert in one confident motion. The halva should release cleanly. Dust generously with ground cinnamon. Serve warm or at room temperature.