Preheat the oven to 400°F. Line a rimmed baking sheet with aluminum foil, and lightly spray with nonstick spray (or lightly oil the foil). Distribute the broccoflower and shiitake mushrooms on the baking sheet. Drizzle with the olive oil. Add the garlic and rosemary sprigs, and sprinkle with salt. Use your hands to combine everything well, then spread the vegetables back over the baking sheet so that they are in a single layer. Roast for about 25 minutes, until the vegetables are just tender, and lightly browned in spots.
While the mixture is in the oven, in a small bowl or container mix together the maple syrup, lemon juice, and vinegar.
Remove the rosemary sprigs from the cooked vegetables and sprinkle over the maple syrup mixture; toss to coat. Taste and season with salt and pepper if needed. Spoon the vegetables into a serving dish and serve hot or warm.