First you need the exact definition of the word infinity, which includes: the quality of being infinite, unlimited extent of time, space, or quantity : boundlessness, an indefinitely great number or amount,
the limit of the value of a function or variable when it tends to become numerically larger than any pre-assigned finite number, a part of a geometric magnitude that lies beyond any part whose distance from a given reference position is finite, a transfinite number, or a distance so great that the rays of light from a point source at that distance may be regarded as parallel.
Some synonyms or related words for Infinity include: everlasting, foreverness, perpetuity, boundlessness, endlessness, interminableness, limitlessness, permanence, permanency, and timelessness.
Next you said this is a fancy restaurant so the words Infinity Restaurant should be in the slogan.
Here are some ideas:
Dine with us at Infinity Restaurant, where truly great food knows no boundaries
Make your reservations with Infinity Restaurant, where flavor is endless (or knows no limits)
Dine at Infinity Restaurant, light years ahead of the competition in quality and flavor
Taking your taste buds to Infinity and Beyond!
Have fun with your 'megalicious' project =)