The a at the end of una is likely to blend into the e of ensalada.
Can you hear the a at the end of ensalada? That should clue you in that the word is most likely feminine and would then take “una.” There are exceptions though, such as “día” which is masculine. We can memorize those though and you can always look up a word in the dictionary to find its gender. https://dictionary.reverso.net/spanish-english/Ensalada The red letters “sf” stand for “sustantivo feminino” or “feminine noun.”
What do you hear after un? It is actually pronounced correctly. The a from "una" will blend with the e from "ensalada". Right away you can see that "ensalada" ends in a and so it is likely to be feminine which would then require "una". When in doubt about the gender of a word, you can look it up in a dictionary. https://dictionary.reverso.net/spanish-english/ensalada The sf in red stands for "sustantivo femenino" which means "feminine noun". Also, when you scroll down you see examples of the use of this word. Memorize articles with words as part of its spelling to remember gender.