Preheat the oven to 400°F/200°C.
For dressing, combine olive oil, lemon juice, and mustard and whisk until thickened. Add dill and parsley, then season with salt and pepper. Add more lemon juice to taste if needed. Set dressing to the side.
Bring a pot of water to a boil. Cut cauliflower into small florets and drop into boiling water. When water returns to a boil, drain cauliflower and put into a bowl.
Drizzle olive oil dressing over the blanched cauliflower florets and toss.
Peel and devein the shrimp. Slice all shrimp lengthwise, cutting each shrimp in half. Toss with 1 Tbsp of extra-virgin olive oil and season with salt and pepper.
Arrange the shrimp in a single layer in an oven-safe dish and bake at 400°F/200°C for 3-5 minutes, or until cooked through. Do NOT overcook. Remove from the oven, discard any liquid, and chill.
Dice cucumber, bell pepper and onions. Slice cherry tomatoes in half. Chop green onions and crumble feta cheese.
Plate all ingredients. Season with salt and pepper. If not served right away, consider adding a squirt of lemon juice to brighten up the flavor.