In pot of boiling salted water, cook fava beans until tender, about 15 minutes. Drain and run under cold water. Transfer to a large serving bowl and toss with broccoli, cauliflower, cucumber, chives and mint.
In small bowl, whisk ricotta, lemon zest, lemon juice, garlic, salt and pepper until combined. Mixture should be thin enough to drizzle; add water, 1 tsp at a time, if needed.
Drizzle ricotta sauce over broccoli and cauliflower tabbouleh, sprinkle with cashews and garnish with lemon wedges.