Mexican Veggie Tortilla stack

• 1 tbsp extra virgin olive oil
• 1 large brown onion, diced
• 2 carrots, grated
• 1 cup corn, frozen
• 800 g tin black beans, drained and rinsed
• 30 g taco seasoning
• 3 tbsp tomato paste
• 5 flour tortillas
• 1 cup shredded cheese
• 1 cucumber, diced
• 2 tomatoes, diced
• 0.5 cup sour cream