Preheat the oven to 425° F.
Place the red bell pepper, garlic cloves and sliced onions in a cast-iron skillet or on a sheet pan. Drizzle with 1 tablespoon olive oil, and salt and pepper.
Roast the veggies for 40 minutes until they are soft and tender and perfectly cooked through.
Meanwhile, heat a grill or grill pan to medium-high heat. Brush the eggplant slices with olive oil and place the eggplant on the grill. Cook for 5 - 7 minutes on each side until soft and grill marks appear.
Add the roasted veggies to a food processor along with the almonds, red wine vinegar, remaining olive oil, honey, and balsamic vinegar. Puree for 1 minute or so until the mixture is smooth. If you like a little crunch, you can pulse it until you reach your desired texture.
When the eggplant and sauce are done, layer the romesco on each eggplant slice, then top with crumbled feta cheese and basil.