basic oil and vinegar dressing starts with 3 parts oil to 1 part vinegar.

then you need some sort of emulsifier to get the oil and vinegar to mix. This is usually dijon mustard stone ground(cooked egg yolk from boiled egg works too).

simple honey mustard dressing:

1 tsp mustard
oil and vinegar in above proportion for total of 1/4 cup
(usually canola oil and red win vinegar. never distilled vinegar)
1 tbs of EVOO
2-3 tsp of honey
pinch of salt
dash of worcester sauce
dash of tabasco
1 tsp of lemon juice

mix vigorously of all ingredients and adjust taste with more oil, vinegar, lemon juice, honey and mustard. Season with cracked pepper.
Play with it.

you can substitute lemon juice with 2 tsp of freshly squeezed orange juice. And if you want with the lemon juice, add fresh herbs like terragon (my fav)

In a burrito, anything goes. It's whatever you like. lettuce, tomato, avocado, sliced radishes, onion, sour cream, cheese, meat, steamed vegi, ...
cumin, chilli powder, jalpeno, salt, pepper, lemon juice...