Preheat oven to 350°F. Place walnuts in a single layer on a small sheet pan. Roast for 6-8 minutes until golden. Once cooled, coarsely chop into smaller pieces. Set aside.
Increase oven temperature to 450 degree. Line a baking sheet with parchment paper.
Remove outer leaves of cabbage, rinse and dry well. Cut off the very end of the stem.
With stem side down, cut 1-inch slices of cabbage from the top down.
Place slices on prepared baking sheet and brush each side with remaining tablespoon of olive oil. Season with salt and pepper to taste.
Roast for 15 minutes. Flip and roast another 15 minutes or until cabbage is tender and slightly charred around the edges.
Meanwhile, make the salsa. Place the capers, sliced garlic (if using) and olive oil in a small saucepan over medium heat. Cook until capers are sizzling and bursting, about 5-6 minutes. Remove from heat, pour into a small bowl, and let cool slightly. Once cooled, add the toasted walnuts, chile (if using), parsley, dried cherries, vinegar, lemon zest, lemon juice, and a pinch of salt. Mix well.
Pour the salsa over the warm cabbage steaks and serve immediately.