Preheat oven to 400°F (200°C). On a baking sheet, toss cauliflower florets with sesame oil, smoked paprika, chili powder, cumin, salt, and pepper.
Roast cauliflower for 20-30 minutes, tossing halfway. Stir in drained black beans during the last few minutes of roasting.
Make the guacamole: In a food processor, combine half an avocado, fresh basil leaves, pine nuts, jalapeño (seeds removed for less heat), and lemon juice.
Pulse until chunky and smooth. Dice the remaining avocado half and stir into the guacamole. Season with salt and pepper.
Heat a small skillet over medium heat with a drizzle of olive oil. Add halloumi slices and cook for 1-2 minutes per side until golden brown and slightly softened. Drain on paper towels.
Assemble tacos: Layer shredded cucumber, roasted cauliflower mixture, and fried halloumi slices into tortillas.
Top generously with the spicy avocado basil guacamole. Enjoy immediately!