Line a rimmed baking sheet with parchment. Lightly brush with oil or coat with cooking spray. Cook sugar, water, and 1/2 teaspoon salt in a heavy medium saucepan over high heat, stirring, until sugar just dissolves. Continue to cook, without stirring, until golden, about 4 minutes. Cook about 1 minute more, swirling the pan, until syrup is light amber. Carefully stir in adobo sauce (hot syrup will spatter), and cook 30 seconds.
Remove pan from heat. Add pepitas, peanuts, and cayenne, stirring to coat. Immediately pour onto baking sheet. Sprinkle with remaining salt. Let cool completely, and break into pieces.
Brittle can be stored in an airtight container up to 2 weeks.