This delightfully unusual salad is a study in pretty colors and delicious textures, hearty enough to be a vegetarian meal.
For a more robust entrée, try adding strips of prosciutto or slices of grilled sausage for additional protein.
Greek haloumi cheese is increasingly available in the deli section of well-stocked supermarkets. It's delicious pan-fried; do it just before serving so the cheese is still meltingly soft, not rubbery.
Be generous with the candied walnuts at the end; they impart a wonderful crunch and a hint of sweetness to balance the salty tang of the cheese and the earthiness of the spinach and beets.
Place the walnuts in a single layer in a skillet. Combine the sugar, sea salt and cayenne in a small bowl. Sprinkle the mixture over the walnuts. Cook over medium heat until the nuts are caramelized, stirring occasionally. Set aside to cool.
To make the dressing, place the vinegar, olive oil, garlic, and a pinch of salt and pepper in a glass jar and seal tightly. Shake to emulsify the dressing. Taste and adjust seasoning as desired. Set aside at room temperature. Leftover dressing can be refrigerated for up to 3 months.
Place the white beans and beets in a large bowl and drizzle with some of the dressing, tossing gently to coat. Add the spinach and toss again, drizzling in more dressing as needed. Transfer the salad to a large platter and garnish with the candied walnuts and avocado slices, if using.
Place a large, heavy skillet (preferably cast iron) over high heat. When the pan is hot, film the bottom with olive oil. Add the slices of haloumi (be sure not to crowd the pan) and cook in batches until the cheese is browned on the bottom side. Using a spatula, carefully flip the cheese and cook the remaining side until golden.
Top the salad with the hot haloumi, drizzle more of the dressing decoratively over the top, and serve immediately.