First, make the dressing. In a food processor or blender, combine the avocado, cilantro, lime juice, water, garlic, green onion, pumpkin seeds, agave, and salt. Process until smooth.
With the processor running on low, slowly stream in the oil until the dressing is creamy and emulsified. Transfer to a jar and chill in the refrigerator while you prepare the salad.
Pat the flank steak dry with paper towels. In a shallow dish, rub the steak all over with oil, lime zest, lime juice, salt, cumin, and paprika.
Heat a large cast-iron skillet or grill pan over medium-high heat. Once hot, add the steak and cook for 4-5 minutes per side for medium-rare.
Transfer the steak to a cutting board and let it rest for 10 minutes before slicing. This allows the juices to redistribute.
While the steak rests, assemble the salad. On a large platter or in a big bowl, combine the chopped romaine, arugula, bell pepper, cherry tomatoes, red onion, black beans, corn, and sliced avocado.
Slice the rested steak thinly against the grain.
Arrange the steak slices over the salad. Garnish with Cotija cheese, pumpkin seeds, and tortilla strips. Serve immediately with the chilled dressing on the side.