In a medium bowl, whisk together large eggs, milk, coarse sea salt, and ground black pepper until well combined and slightly frothy.
Preheat a Blackstone griddle to medium-high heat.
Add breakfast sausage, diced bell pepper, and diced small onion to one side of the griddle. Cook for 5 to 7 minutes, breaking up the sausage as it cooks, until the sausage is browned and the vegetables are tender.
Drizzle 1 tablespoon oil onto the other side of the griddle and reduce that section to medium-low heat.
Pour the egg mixture onto the oiled side of the griddle. As the eggs begin to set, use a spatula to gently pull the cooked eggs from the edges toward the center. Continue cooking, stirring occasionally, until the eggs are set but still soft.
Stir the cooked sausage, bell pepper, and onion mixture into the eggs and reduce the heat to low.
Place 12 street taco tortillas on the hotter side of the griddle and warm for about 30 seconds per side, or until soft and pliable.
Divide the sausage and egg mixture evenly among the 12 warmed tortillas.
Top the tacos with shredded Colby Jack cheese, salsa, diced avocado, and chopped fresh cilantro.
Add any desired optional toppings, including diced jalapeños, sliced green onions, crumbled cooked bacon, diced tomatoes, hot sauce, or Pepper Jack cheese.
Serve immediately.