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1
Lightly grease a 9-by-13-inch baking dish.
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2
Line a baking sheet with foil.
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3
Cook the spaghetti according to the package instructions in a large pot of boiling salted water.
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4
Drain, rinse, and transfer the spaghetti to the baking dish.
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5
Meanwhile, turn on the broiler and place a rack 6 inches away from the heating element.
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6
Place the grape tomatoes and jalapenos on the prepared baking sheet, skin side up, along with the whole garlic cloves and onion.
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7
Broil, for 5 to 7 minutes, until the tomatoes, jalapenos, garlic, and onion are softened and have begun to blacken.
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8
Remove from the oven, and when cool enough to handle, dice the tomatoes, jalapenos, garlic, and onion.
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9
Turn the oven temperature down to 350 degrees F.
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10
To make the sauce for the spaghetti, in a saucepan, melt the butter over medium-low heat.
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11
Whisk in the flour until well combined and slightly browned, about 30 seconds.
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12
Slowly pour in the milk and cook, stirring, until the sauce thickens just a bit, 3 to 5 minutes.
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13
(You want it to coat the back of your spoon, but not be too thick, like custard.
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14
If it gets too thick, you can slowly add more milk, about a teaspoon at a time.)
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15
Once the sauce thickens, immediately turn off the heat and slowly stir in half of the cheeses, about 1/4 cup at a time, until melted and incorporated into the sauce.
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16
Stir in the diced vegetables, along with the cumin, cayenne, cilantro, and lime juice.
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17
Taste and adjust the seasonings, adding salt and black pepper to taste.
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18
Pour the sauce into the cooked spaghetti and then stir in the shredded cooked chicken.
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19
Cover the spaghetti with the remaining cheeses.
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20
Bake, uncovered, for 20 minutes, or until brown and bubbling.
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21
Garnish with cilantro before serving.
