In a small saucepan, heat vegetable stock to a vigorous simmer.At the same time, set a wide 2-quart saucepan over medium/medium-high heat. Add olive oil. When oil starts to shimmer, add couscous. Cook stirring almost constantly until the couscous is golden and smells nutty, 3 - 5 minutes. Edge heat down or pull pan from heat if it starts to burn. Stir hot stock into couscous, add 1/2 teaspoon sea salt, stir, cover, and turn heat to low. Cook 10 minutes, or until couscous is cooked through and all the water is absorbed, fluff with a spoon, and cool for 10 minutes.To make dressing, use a fork to combine lemon juice, sherry vinegar, and sea salt. Whisk in olive oil.To plate the salad, toss couscous, herbs, greens, and green onions with half the dressing. Taste and add sea salt as needed. Arrange in a bowl, scatter feta on top, and cover a section with tomatoes. Finish the tomatoes with a generous pinch of sea salt and a twist or two of pepper, and serve.Toss leftovers together in a big container. Salad will keep well sealed in the fridge for 5 days.