Roast the poblano pepper until blistered.
Let it cool, then remove the skin and seeds.
Dice it and set it aside.
In a medium skillet, heat olive oil over medium heat.
Add the chopped red onion and minced garlic.
Cook until the onion is translucent.
Stir in the diced poblano pepper, jalapeño, and tomatoes.
Cook for about 5 minutes.
Reduce the heat and slowly add milk to the mixture, stirring continuously.
Gradually incorporate both the cheddar and Monterey Jack cheeses.
Stir until fully melted and smooth.