Sear the plums: Heat a frying pan over medium heat with a little of 2 teaspoons neutral oil for frying (vegetable, canola, or avocado). Add 2 plums, cut into wedges and 2 sprigs fresh thyme. Let plums color and soften slightly, then stir in 1 tbsp of 2 tablespoons honey. Once caramelized, turn off heat and set pan aside.
Sear the halloumi: Preheat a non-stick frying pan over medium heat with a little of 2 teaspoons neutral oil for frying (vegetable, canola, or avocado). Pat 1 block halloumi cheese, sliced dry with a cloth, then carefully add to the pan.
Build the seed-and-honey crust: Color the halloumi on both sides until golden. Stir in 1 teaspoons sesame seeds, 1 teaspoons nigella seeds, and 1 teaspoons fennel seeds, then the remaining 2 tablespoons honey. Turn heat down low and let bubble gently, then turn off heat and let cool slightly.
Make the dressing: Remove halloumi from the pan and set aside. Stir 1 tablespoons red wine vinegar, any leftover liquid from the plum pan, and 1 tablespoons olive oil into the now-empty halloumi pan to form a dressing. Use this to dress 2 big handfuls washed mixed salad greens.
Assemble and serve: Divide dressed salad greens between two bowls. Top with halloumi, plums, 4 slices red onion, and 6 fresh tarragon leaves, washed. Finish with 1 tablespoons toasted hazelnuts, roughly chopped and season with 1 pinch salt and pepper, to taste. Serve immediately.