For the onions: Melt the butter in a skillet over medium-low heat. Add the red onions and cook slowly, stirring occasionally, until soft and deep golden brown, 10 to 15 minutes. Set aside and let cool slightly.
For the hummus: Meanwhile, combine the chickpeas, tahini, cumin, garlic, lemon juice and some salt in a blender. Pulse until the mixture becomes somewhat smooth and combined, but do not overmix. Add 1/2 to 1 cup cold water as needed to facilitate blending and reach the desired consistency. Add the olive oil and pulse a few more times just to incorporate. Taste and add more cumin, salt or garlic if needed. Pour the hummus into a bowl and stir to ensure it's combined. Serve immediately, or refrigerate for up to 3 days.
For the balsamic vinaigrette: Shake together the oil, vinegar and some salt and pepper in a Mason jar. This makes more than you'll need for 1 wrap; store the rest in the fridge and use for another salad.
For the wrap: Grill the tortilla on a grill pan over medium heat just until it has grill marks on the outside, 1 minute. (If you don't have a grill pan, just use a skillet.) The tortilla should still be soft and pliable, with just a little bit of color! Let the tortilla cool slightly.
To assemble the wrap, spread about 1/4 cup of the hummus down the middle third of the tortilla. Arrange the cooked onions and roasted red peppers all over the hummus. Add the artichoke heart halves. Toss the salad greens in 1 tablespoon of the balsamic vinaigrette, then lay them on the wrap. Finally, sprinkle the crumbled feta all over the greens. Carefully wrap up the tortilla, tucking in the ends. Slice the wrap down the middle, share with a friend and chow down!