In a large skillet over medium heat, add the vegetable oil and sauté chopped onions until translucent, about 3–4 minutes.
Add the shredded brisket and stir until heated through.
Lower the heat and add Velveeta cheese cubes, stirring constantly until melted and smooth.
Stir in Rotel tomatoes, garlic powder, and cumin. Mix well.
Add milk a little at a time if you prefer a thinner consistency.
Simmer on low for 5–7 minutes, stirring occasionally.
Serve warm, garnished with fresh cilantro and a side of tortilla chips.