If they really are Southern Indian, I would unhesitatingly go for the masala dosa and some of the numerous vegetarian starter options that are likely to be offered (examples below); I am a 100% carnivore, but Southern Indian vegetarian cuisine is an art-form that even I can appreciate.
** Phil.
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Upuma
Lightly fried semolina with onions and spices
Aloo Bonda
Traditional spicy creamed potato balls in a light batter
Mendu Vadai with Sambar
4 pieces served with chutney
Masala Vadai or Mendu Vada
A spicy cutlet or a spicy donut
Iddly Sambar
Lightly steamed ground-ricecakes served with tasty sambar and chutney
Sambar
A tasy savoury gravy, cooked with lentils, vegetables and tamarind juice
Adai and Avail
Delicious lentil pancake served with temperedvegetables cooked with coconut and butter
Uthappam
Thick golden brown rice lentil pancakes topped with fresh tomatoes, onions, green chillies and ginger
Rasam
A soup consisting of tamrind juice, black pepper, frsh tomatoes, green chilli, garlic and ginge.
Dahi Vadai
A lentil donut marianted in lightly spiced yoghurt