Grilled Stuffed Cubanelle Peppers

6 medium Cubanelle peppers6 tsp olive oil, divided2 cloves garlic, minced1 cup whole-wheat Israeli couscous1 small yellow zucchini, cut into strips1/2 cup each cooked romano beans and chickpeas (aka garbanzo beans; or BPA-free no-salt-added canned beans, drained and rinsed)1/2 cup crumbled feta cheese1/4 cup sliced sun-dried tomatoes (not packed in oil)1/4 cup coarsely torn fresh basil (about 5 medium leaves)2 tbsp white wine vinegar1/4 tsp fresh ground black pepper1/4 tsp sea salt, optionalPreheat grill to medium-high.Cut tops off peppers, about 1/2 inch. Remove and discard stem and seeds. Dice tops of peppers and transfer to a medium bowl. Set aside bowl and cored peppers.In a small saucepan, heat 1 1/2 tsp oil on medium-high. Add garlic and couscous and stir until garlic is light golden and fragrant. Add 2 cups water and bring to a boil. Reduce heat to low, cover and steam for 8 to 10 minutes, until all liquid is absorbed and couscous is al dente. Remove from heat and let stand, covered, for 5 minutes. Remove lid and fluff with a fork.Meanwhile, grill peppers and zucchini: Grill cored peppers for about 8 minutes, turning occasionally until all sides are lightly charred. Remove peppers from grill and allow to cool at room temperature. Brush zucchini with 1/2 tsp oil and grill for 2 to 3 minutes, turning once, until lightly charred and tender. Let zucchini cool slightly, dice and add to bowl with diced pepper tops.Add couscous, beans, chickpeas, feta, tomatoes, basil, vinegar, remaining 4 tsp oil, black pepper and salt, if desired, to pepper-zucchini mixture. Mix well.Stuff about 3/4 cup pepper-zucchini mixture into each grilled pepper; lightly pack filling throughout entire pepper until filling reaches the top. Wrap each pepper tightly with plastic wrap and refrigerate for a minimum of 1 hour or a maximum of overnight. (Alternatively, carefully lay stuffed peppers in a shallow tray or dish, cover and refrigerate.)To serve, arrange peppers on a platter and serve.