1. In a large skillet, toast the farro over medium-high heat. Shake the skillet occasionally, until the farro is aromatic and slightly golden (about 2 minutes).
2. Transfer the toasted farro to a medium saucepan. Cover with 1 inch of water; bring to a simmer over medium-high heat. Reduce heat to medium-low, and cook, uncovered, until farro is tender (20-25 minutes). Drain farro, and transfer to a large serving platter to cool at room temperature.
3. In a small bowl, combine the reserved roasted bell pepper liquid, vinegar, olive oil, salt, and black pepper; stir well with a whisk. Set the vinaigrette aside.
4. Preheat a grill to medium-high. Grill the zucchini slices until tender (about 2 minutes per side); transfer to platter with the farro.
5. Arrange butter beans and roasted bell peppers over farro; drizzle with vinaigrette.
6. Sprinkle the farro and vegetables with sliced fennel and fronds and Parmesan cheese; drizzle with more vinaigrette as desired. Serve at room temperature.