Preheat the oven to 180°C | 356°F. Line two baking trays with baking paper or aluminium foil; set aside.
Combine half of the butter and sage leaves in a small saucepan (or skillet), and melt over high heat. Allow butter to bubble away for about 3 minutes, or until fragrant.
On the first tray; combine the diced pumpkin, garlic and bacon together. Sprinkle with salt to season; drizzle over the melted butter and oil, and toss to evenly coat. Roast for 30 minutes, mixing pumpkin around once during cooking. Sprinkle over the goats cheese, change oven setting to grill (or broil) on medium heat and continue to cook until pumpkin is slightly crispy on the edges and soft in the centre.
While pumpkin is roasting, place the portobellos on the second tray (upside down); spray with cooking oil spray, and roast in the oven for 20 minutes. Once roasted, drain any liquid from inside the caps and set aside. (If you can fit both trays in the oven, they can be roasted at the same time.)
Meanwhile, combine remaining butter and sage leaves in the same pan/skillet over high heat. When butter melts and starts to bubble, reduce heat to medium and continue to bubble, while occasionally stirring, until the butter begins to change in colour and smells 'nutty'. Remove from heat immediately to prevent burning.
Divide the pumpkin/bacon mixture by 4 and spoon into each portobello cap. Drizzle the browned butter over the top and garnish with the crisped sage leaves.