Bring a pot of lightly salted water to a boil while you cut up broccoli and cauliflower into bite-sized pieces.
When water boils, add the cauliflower and cook 1 minute.
Then add the broccoli and cook 2-3 minutes more, just until veggies are barely starting to get tender. (Test a piece with a fork.)
When veggies are done, drain in a colander placed in the sink. Let them drain well, or pat dry with paper towels if you're in a rush.
While veggies drain and come to room temperature, chop the red onion and crumble the Feta.
Zest the lemon and squeeze the juice.
Chop the fresh tarragon, or other herbs of your choice.
Whisk together the olive oil, mayo, lemon zest, lemon juice, Dijon, chopped tarragon, Spike Seasoning and salt and pepper to make the dressing.
When broccoli and cauliflower is at room temperature, toss with desired amount of dressing.
Then gently mix in the red onion.
Carefully fold in the Feta cheese and season salad to taste with salt and fresh-ground black pepper.
Serve salad at room temperature.
Leftovers of the Broccoli Cauliflower Salad will keep in the fridge for a day or two, but the salad is definitely best when it's freshly made.