Toasting whole spices deepens and opens up their flavors, perfuming and flavoring this dressing. Use leftover dressing as a marinade for chicken or fish.
Toast coriander, cumin, and fennel in a small skillet over medium, stirring often, until fragrant, about 3 minutes. Remove from skillet; let cool 5 minutes. Transfer mixture to a spice grinder, and process until finely ground, about 10 seconds (or finely crush spice mixture using a mortar and pestle). Whisk together ground spices, oil, vinegar, lemon juice, mustard, salt, and pepper in a small bowl. Cover and chill until ready to use, up to 3 days.
Preheat oven to 400°F. Toss together bread, oil, and salt on a rimmed baking sheet lined with parchment paper until evenly coated. Bake in preheated oven until golden brown, 10 to 15 minutes, stirring once halfway through bake time.
Place lettuce leaves and half of the croutons in a large bowl; add dressing, and toss to coat. Transfer salad to a large platter; sprinkle evenly with edible flowers, herbs, and remaining croutons.
Tarragon-scented, lemony Sauvignon Blanc.