Green beans on toast

Name: Green beans on toast
Cuisine: European
Ingredients: 100ml olive oil; 2 small banana shallots, thinly sliced (75g); 4 garlic cloves, thinly sliced; 300g French beans, trimmed; 300g runner beans, trimmed and cut on the diagonal into 2cm strips; 100g cherry tomatoes, halved; 1½ tsp dried oregano; ½ tsp chipotle chilli flakes; 1½ tbsp lemon juice; 1½ tbsp fresh oregano, roughly chopped, plus extra leaves to garnish; 10g basil leaves, roughly torn, plus extra to garnish; 100g feta, roughly crumbled; 100g mascarpone; 4 thick slices of sourdough, toasted (200-225g); salt and black pepper